A code division multiple access (CDMA) system is an interference limited system in that the total system capacity is limited by the interference level. For the return link or uplink of a satellite CDMA system (the link back to the satellite gateway from a user terminal), interference management is critical to prevent system overload. Conventional methods of interference management are typically based on a direct interference measurement or allow a certain maximum number of terminals using an equivalently same data rate (e.g., voice data rate) to be connected. See, e.g., Vanghi, Damnjanovic, and Vojcic, “The CDMA2000 System for Mobile Communications,” Prentice Hall, Upper Saddle River, N.J., 2004. In the direct interference measurement method, the interference level is continuously measured at the receiver, and the user terminal transmissions are controlled to maintain the total received interference at the receiver within a certain limit. Alternatively, the number of terminals in transmission at any given time can be counted to sum up the total interference, assuming that each terminal generates a relatively equivalent amount of interference, and then the total summation is controlled to be within the limit.
Challenges may arise, however, when user terminals (UTs) within the same beam coverage are connected to multiple gateways. One gateway may have only the knowledge of terminals connected to it. As such, when sharing the same return link frequency resource at the same time, each of the gateways makes the decision of admitting a UT independently based on the maximum number of channels a gateway can accommodate on a certain frequency band. Consequently, this may result in overloading the system. Interference may also result from terrestrial wireless equipment transmitting on the same frequency as the satellite link, which cannot be known to the gateway. Additionally, in a multiple gateway system, the total number of concurrently active channels may be unknown to any of the gateways, thus rendering it difficult and impractical to apply the conventional methods for a satellite CDMA system when multiple gateways cover the same beam area. Accordingly, in a satellite CDMA system, conventional direct interference measurement methods can be inaccurate and thus make it difficult (if not impossible) to maintain the interference within necessary limits and not overload the system.
Moreover, for quality of service (QoS) provisioning, it is also important that the gateways are aware of and able to manage the interference level of the covered beams. UTs with different traffic types may be provided with differentiated QoS. For example, real-time voice and video may have higher priority than other non-real-time data communications in obtaining network resources (e.g., bandwidth). The interference level is a function of the network traffic load (e.g., higher total traffics load could result in higher interference), and thus managing interference can be achieved via admission control with differentiated QoS provisioning.
What is needed, therefore, is an approach that provides for effective estimation and control of the overall interference level of a satellite communications system (e.g., a CDMA satellite system) within a range to prevent system overload, without using direct interference measurements, and which permits each individual gateway to make admission decisions autonomously.